Development of diazotype papers without a coupler



United States Patent 3,331,690 DEVELOPMENT OF DIAZOTYPE PAPERS WITHOUT A COUPLER George W. Pope, Lexington, and Francis R. Clarke, Nicholasviile, Ky., and George R. Jurch, .lr., San Diego, Calif., assignors to International Business Machines Cor oration, New York, N.Y., a corporation of New York No Drawing. Filed June 8, 1964, Ser. No. 373,549 8 Claims. (Cl. 96-49) ABSTRACT OF THE DISCLOSURE This invention relates to the production of photographic prints from light-sensitive diazo materials. More particularly, this invention relates to new and useful lightsensitive diazotype compositions, to photographic materials coated therewith, and to methods of using said photographic materials.

The use of organic compounds as light-sensitive media for photographic purposes is well known, and is perhaps best exemplified by the diazo process. This process is based on the photochemical changes effected in various diazonium salts upon exposure to light, and which atfect their capacity to form dyes. In general, dyes are formed when the diazonium compounds, or diazotized amines, couple with phenols or aromatic amines in an alkaline medium. Upon exposure to light, the diazonium compounds undergo decomposition and are rendered incapable of forming the corresponding dyestuffs through the coupling process. After light exposure and development, a dyestulf is formed at the portions of the lightsensitive material which have not been exposed to light (i.e., at portions on the light-sensitive material which have been protected by the pattern or design on the material to be copied) and thus a positive record is obtained from a positive image.

In diazotype processes used for the reproduction of documents, two methods of development are used, the so-called dry development with gaseous ammonia and the so-called semi-wet development with alkaline solutions containing among other things the azo dye coupling component or coupler. Consequently, there are also two types of light sensitive material suitable for the diazotype reproduction processes, to wit, two component material for the dry development process and one component material for the semi-wet development process. In the case of the dry development material, the azo dye coupling component is present in the light-sensitive coating and not in the developing material. In the case of the semiwet materials, the azo dye coupling component is present in the developer but not in the light-sensitive material. It is understood that the two essential components are the light sensitive diazo compound and the azo dye coupling component.

In the wet development process, it has been the practice to employ an alkaline, buttered aqueous solution containing a coupler that is applied to a diazotype paper after light exposure. This results in the azo-dye formation at the areas of the light-sensitive material which have not 3,331,690 Patented July 18, 1967 been light exposed. This method, however, has the following disadvantages:

(1) The coupler in the alkaline aqueous solution is easily oxidized because of the basicity of the solution. This produces a developing solution which discolors the diazo paper during development thereof.

(2) The coupling solutions utilized in the wet development systems are saturated with the necessary ingredients. Use thereof results in the precipitation of various solids from the solution because of the decrease in the ambient temperature and/or the evaporation of the solvent (i.e. water).

(3) The coupling solutions usually contain a mixture of ingredients which are selectively absorbed by the copying paper during the development process. This results in non-uniform color reproduction as the solution is used during a given period.

(4) The handling of the corrosive solutions is difficult and hazardous.

(5) The dye formed by the diazo and the coupler must be wash-fast, since it is formed under wet conditions which are favorable to bleeding.

In the dry development process, it has been the practice to utilize gaseous moist ammonia applied to the light exposed diazotype paper as developing agent. In various instances, a second sheet (i.e., the developer sheet) is impregnated with an alkaline generating material which when heated will yield ammonia by decomposition. In other Words, this method contemplates the utilization of merely two sheets of paperone containing the latent image in the form of unreacted diazo and diazo coupling components and the other containing a compound which under proper conditions releases an alkalyzing medium in direct contact with the imaged surface to develop the latent image by promoting the coupling reaction through the adjustment of the ambient pH con ditions. Since both the diazo compound and the coupler are intimately mixed in the same layer, it is clear that severe restrictions are placed on the choice of the diazo coupler if premature coupling is to be avoided. Precoupling frequently takes place after relatively short storage periods with the result that the background areas are no longer white but badly discolored.

It is therefore an object of the present invention to overcome the disadvantages of the diazotype coupling processes and to permit coupling to occur without the necessity of providing a coupling component.

It is an object of the present invention to describe an improved process for the production of diazotype materials which does not require an azo coupling component.

It is an object of the present invention to provide improved diazotype materials having increased storage life.

It is an object of the present invention to provide improved diazotype materials having increased storage life and which contain no coupling component. i

A further object is to provide a dry diazotype sheet having a light-sensitive coating thereon, and where said material has good storage characteristics.

A further object is to provide a dry diazotype sheet having a light-sensitive coating thereon, and which coating has no coupling component incorporated therein.

These and other objects and advantages of the present invention will be apparent from the following discussion, and as such are intended to be objects thereof, whether enumerated or not.

These and other objects are accomplished by coating a suitable substrate with a composition containing the cation of a light-sensitive diazonium salt. A zinc chloride stabilizer is preferably used to provide stability inthe manner well understood in the art. Of course, suitable other or equivalent adjuvants such as citric acid, oxalic acid,

a mixture of diazonium salts is not necessary.

After the substrate is coated with the aqueous diazonium solution, the material is dried. Upon exposure to light, the portions of diazonium compounds exposed to light undergo decomposition and, therefore, are incapable of forming conjugated, colored compounds. A latent image exists on the diazonium coated substrate. During development, a dyestuif is formed at the portions of the light-sensitive material which have not been'exposed to light (i.e., at portions on the 1ight-sensitive material to be copied) and thus a positive record is obtained from a positive image.

In accordance with the invention the diazonium material containing a latent image is treated with ammonium, a primary aliphatic amine, or a secondary aliphatic amine. These materials contain electron rich centers and also at least one hydrogen directly bonded to a nitrogen. It is believed that they join with the positive diazo group with the expulsion of a hydrogen to form the more stable aromatic azo compound. Ammonia and primary aliphatic amines form azo compounds in which the nitrogen which was originally part of the ammonia or amine still contains an electron rich center and a directly bonded hydrogen. Such a nitrogen is believed to join once again with a diazo group to form a symmetrical azo compound with five nitrogen molecules in a chain. This is described by the following formulas, where AR is an aryl radical and R is aliphatic.

A preferred formula contains p-diazo-N-morpholino-2, S-diethoxybenzene chloride-half zinc chloride salt, pdiazo-N-ethyl-N-benzylaniline chloridehalf zinc chloride salt, and citric acid using water as a solvent. The solution is coated on the paper and dried at a temperature between 70 and 140 F. Upon exposure of the sensitized paper to suitable radiant energy through a master (such as a letter typed on 20-pound bond paper) and treatment of the exposed coating with warm moist ammonia fumes, an image of the original is produced. The combined diazo compounds yield a very satisfactory, near black color. Since no coupler or basic ingredient need be present in the formula which is coated on the substrate, the stability of the unexposed material is substantially improved.

Example I The following solution was coated on paper to a wet thickness of about 1 mil and dried. This gave a concentration of about 0.75 grams of diazo per, square meter. When exposed to light and developed with moist aqueous ammonia, a brown image was produced.

Grams 4 In 100 grams of water the ingredients may vary in the following amounts:

G./M coated Example II The diazo of Example I can be replaced by one of the following diazos:

(A) P-diazodimethylaniline zinc chloride-after exposure to light and development, a brown image is produced.

(B) 4-N-morpholino-2,5-diethoxybenzene diazonium zinc chlorideafter exposure to light and development, a reddish brown image is produced.

(C) P-diazo-N-benzyl-N-ethylaniline zinc chloride after exposure to light and development, a brown image is produced.

(D) P-diazo-2,5-dibutoxy benzoylaniline zinc chlorideafter exposure to light and development, a brown image is produced.

Example III The acid of Example I can be replaced by citric acid, 1-6 grams per 100 grams of water or oxalic acid 1-4 grams.

Example IV The thiourea may be left out or replaced by one of the substituted thioureas such as 1-allyl-2-thiourea and stabilizers such as naphthalene-1,3,6-trisodium sulfonate may be used.

Example V Mixtures of two or more diazonium salts may be used to improve the shade of the color obtained. The following is an example illustrating such a composition:

Grams P-diazo-N-ethyl-N-benzylaniline zinc chloride 2 4-N-morpholino-2,5-diethoxybenzene diazonium chlo- When ammonia developed, this produced a near black image.

It should be noted that the use of background stabilizers, such as thiourea, and diazo stabilizers, such as naphthalene-1,3,6-trisodiu-m sulfonate, While advantageous to the over-all effect of producing an excellent image, are not necessary for the proper accomplishment of the objects of the present invention. Additionally, while the above examples have disclosed the utilization of ammonia as the specific developing agent, equivalents, whether gaseous or in solution, are considered to be applicable for utilization in the development of the present invention.

The primary amines, n-butyl amine and benzyl amine, have been reacted with 4-diethylaminobenzene diazonium zinc chloride with entirely satisfactory formation of color.

Colors formed by development with primary amines do not What is claimed is: 1. A process for development of a visual image in the 5 absence of an azo-coupling component which comprises:

exposing a light-sensitive material to light under a pattern, said light-sensitive material being a layer consisting essentially of a mixture of light-sensitive diazonium salts, said mixture comprising the cation of a p-diazo-N-ethyl-N benzylaniline salt and the cation of a 4-N-morpholino-2,5-diethoxy benzene diazonium salt, and

thereafter developing the latent image with a material selected from the group consisting of ammonia, primary aliphatic amines, and secondary aliphatic amines.

2. The process of claim 1 wherein the developing material is ammonia.

3. The process of claim 1 wherein the developing material is a primary aliphatic amine.

4. The process of claim 1 wherein said mixture of di- 5. The process of claim 4 wherein the developing material is ammonia.

6. The process of claim 4 wherein the developing material is a primary aliphatic amine.

7. The process of claim 5 wherein said mixture of diazonium salts is in'the proportion of about two-thirds 6 parts by weight of said 4-N-morpholino-2,S-diethoxyben- Zene diazoniurn salt to one-third parts by Weight of said p-diazo-N-ethyl-N-benzylaniline salt.

8. The process of claim 6 wherein said mixture of diazonium salts is in the proportion of .about two-thirds parts by weight of said 4-N-morpholino-2,5-diethoxybenzene diazonium salt to one-third parts by Weight of said p-diazo- N-ethyl-N-benzylaniline salt.

References Cited UNITED STATES PATENTS 2,308,058 1/ 1943 Crowley et al. 9649 2,793,118 5/1957 Sanders ct al 9675 X 3,064,049 11/1962 COX 9691 X 3,069,268 12/1962 Herrick 9675 X 3,081,166 3/1963 Van Loon et al 96 91 X 3,113,025 12/1963 Bialczak 9649 X 3,138,460 6/1964 Levinos 9649 X 3,163,535 11/1964 StraW 9675 3,164,469 1/1965 Behmenburg et a1. 9691 X OTHER REFERENCES Benbrook, C. H.: American Documentation, vol. 8, The Diazo-Type Process, pp. 86 relied on.

Kosar, Jaromir: Photographic Science and Eng, vol. 5, No. 4, Thermal Development of Diazotype Papers, pp. 239243 relied on.

NORMAN G. TORCHIN, Primary Examiner. C. L. BOWERS, JR., Assistant Examiner. 

1. A PROCESS FOR DEVELOPMENT OF A VISUAL IMAGE IN THE ABSENCE OF AN AZO-COUPLING COMPONENT WHICH COMPRISES: EXPOSING A LIGHT-SENSITIVE MATERIAL TO LIGHT UNDER A PATTERN, SAID LIGHT-SENSITIVE MATERIAL BEING A LAYER CONSISTING ESSENTIALLY OF A MIXTURE OF LIGHT-SENSITIVE DIAZONIUM SALTS, SAID MIXTURE COMPRISING THE CATION OF A P-DIAZO-N-ETHYL-NBENZYLANILINE SALT AND THE CATION OF A 4-N-MORPHOLINO-2,5-DIETHOXY BENZENE DIAZONIUM SALT, AND THEREAFTER DEVELOPING THE LATENT IMAGE WITH A MATERIAL SELECTED FROM THE GROUP CONSISTING OF AMMONIA, PRIMARY ALIPHATIC AMINES, AND SECONDARY ALIPHATIC AMINES. 